The broad objective of this proposal is to elucidate the calcium- dependent mechanisms of nicotinic receptor function. It was recently shown that neuronal nicotinic receptors (nAChRs) have a high Ca2+ permeability and our initial studies indicate that changes in calcium homeostasis and Ca2+/calmodulin-dependent protein kinase (CaM- Kinase II) can modulate nicOtine's pharmacological effects and are involved in neuroadaptative processes after chronic exposure to nicotine in the animal. In this project we plan to study calcium-dependent intracellular mechanisms and their modulation after short and long-term activation of nAChRs. We will assess the potential role of CaM-kinase II activatiOn in the behavioral effects of nicOtine using pharmacological, biochemical and genetic approaches. Tolerance to nicotine's effects could involve an adaptation in the calcium signaling system activated by nicotine leading to a decrease in in CaM-kinase II activity. Such a hypothesis will be investigated by measuring quantitative and qualitative changes in Ca2+-calmodulin-dependent signaling in in vitro and ex-vivo preparations during long-term exposure to nicotine. Finally, we will attempt to modulate tolerance to nicotine's effects by administering drugs that alter calcium entry. In vivo studies with calcium channel modulators and CaM-Kinase II inhibitors as well as NMDA receptor antagonists will be conducted in animals chronically infused with nicotine. The proposed studies will elucidate the calcium-dependent processes involved in nicotine's actions in the brain as well as the neuroadaptation that occurs after short-and long-term exposure to this drug of abuse.